1. Field of the Invention
The present invention relates to a pressure differential motor control system and method for use in connection with high volume low pressure (HVLP) spraying systems, specifically in controlling motor speed by pressure differential.
2. Description of the Prior Art
Pressure differential motor control system and methods are desirable for controlling motor speed in HVLP spray systems dependent on trigger operation thereby extending component life by significantly reducing the heating effects experienced by constant high speed running of the motor.
The use of a HVLP air pressure control system is known in the prior art. The standard turbine base HVLP unit has a vacuum cleaner-like motor as an air pressure source, a hose connected to the air pressure source, and a spray gun attached to the hose. When the HVLP unit is on, the motor is constantly running which provides a constant air flow to the spray gun, which is known to one skilled in the art as a bleeder where the trigger has no effect of airflow from the air pressure source. Lower cost turbines run at a constant full speed, while more advanced and costly units may have a number of fixed speeds, or a fully variable speed with a common design theme being that the motor runs at a constant speed whether the gun is spraying or not.
Market conditions have led to the need of a spray gun system which blocks the flow of air when the spray gun trigger is released, which is known to one skilled in the art as a non-bleeder type spray system. Blocking the airflow results in the air supply motor heating considerably while the system is in a trigger-released condition. This solution is inexpensive at the time of purchase, but has led to increased motor failure and increased maintenance costs.
Most HVLP manufacturers have placed some type of vent, blow off valve or similar discharge device between the turbine/motor and spray gun to release a portion of the air pressure, and as a result have somewhat elevated temperatures and potentially reduced motor life caused by this condition. One disadvantage of this approach is that it may result in some loss of pressure at the spray gun if the vent is a simple orifice or if the vent valve tends to remain open (percolates). Another disadvantage is that since many of these discharge devices are externally mounted, there is the possibility of removal by the operator, being damaged, or being blocked, which could significantly reduce turbine motor life.
The elevated temperatures experienced during trigger closed condition is exacerbated by units which have operating pressures toward the higher end of the 0-10 PSI range. Frequently this pressure is generated by turbine motor(s) having multiple stages, but may be also generated by comparable prime movers or motors that will also have similar heating effects at these pressures when the airflow is blocked.
Some HVLP units have incorporated a motor control device which uses airflow measurements. These units measure airflow by direct method, such as impingement on a valve plate, or a dual valve system with one of the valves in the spray gun. In these units sensitivity is limited to calibration of a spring tension against the available force on the valve plate, hence integration of a system to variable speed electronics (feedback loop) would be difficult due to this design. It can be appreciated that because the valve physically opens and closes, the restriction to airflow is variable thus can cause inconsistent results with the spray gun.
While the above-described devices fulfill their respective, particular objectives and requirements, the aforementioned patents do not describe a pressure differential motor control system and method that allows controlling a HVLP motor by pressure differential. The above-identified patents make no provision for the use of a venturi to create a pressure differential which is detected and converted into a signal that is used to control motor speed. Furthermore, the present invention has all the advantages of a non-bleeder spray gun system with reduced noise and power consumption, and increased motor life.
Therefore, a need exists for a new and improved pressure differential motor control system and method that can be used for controlling a HVLP motor by pressure differential. In this regard, the present invention substantially fulfills this need. In this respect, the pressure differential motor control system and method according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provide an apparatus primarily developed for the purpose of controlling a HVLP motor by pressure differential.